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1.8 |
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09-Apr-2022 |
riastradh |
Introduce membar_acquire/release. Deprecate membar_enter/exit.
The names membar_enter/exit were unclear, and the documentation of membar_enter has disagreed with the implementations on sparc, powerpc, and even x86(!) for the entire time it has been in NetBSD.
The terms `acquire' and `release' are ubiquitous in the literature today, and have been adopted in the C and C++ standards to mean load-before-load/store and load/store-before-store, respectively, which are exactly the orderings required by acquiring and releasing a mutex, as well as other useful applications like decrementing a reference count and then freeing the underlying object if it went to zero.
Originally I proposed changing one word in the documentation for membar_enter to make it load-before-load/store instead of store-before-load/store, i.e., to make it an acquire barrier. I proposed this on the grounds that
(a) all implementations guarantee load-before-load/store, (b) some implementations fail to guarantee store-before-load/store, and (c) all uses in-tree assume load-before-load/store.
I verified parts (a) and (b) (except, for (a), powerpc didn't even guarantee load-before-load/store -- isync isn't necessarily enough; need lwsync in general -- but it _almost_ did, and it certainly didn't guarantee store-before-load/store).
Part (c) might not be correct, however: under the mistaken assumption that atomic-r/m/w then membar-w/rw is equivalent to atomic-r/m/w then membar-r/rw, I only audited the cases of membar_enter that _aren't_ immediately after an atomic-r/m/w. All of those cases assume load-before-load/store. But my assumption was wrong -- there are cases of atomic-r/m/w then membar-w/rw that would be broken by changing to atomic-r/m/w then membar-r/rw:
https://mail-index.netbsd.org/tech-kern/2022/03/29/msg028044.html
Furthermore, the name membar_enter has been adopted in other places like OpenBSD where it actually does follow the documentation and guarantee store-before-load/store, even if that order is not useful. So the name membar_enter currently lives in a bad place where it means either of two things -- r/rw or w/rw.
With this change, we deprecate membar_enter/exit, introduce membar_acquire/release as better names for the useful pair (r/rw and rw/w), and make sure the implementation of membar_enter guarantees both what was documented _and_ what was implemented, making it an alias for membar_sync.
While here, rework all of the membar_* definitions and aliases. The new logic follows a rule to make it easier to audit:
membar_X is defined as an alias for membar_Y iff membar_X is guaranteed by membar_Y.
The `no stronger than' relation is (the transitive closure of):
- membar_consumer (r/r) is guaranteed by membar_acquire (r/rw) - membar_producer (w/w) is guaranteed by membar_release (rw/w) - membar_acquire (r/rw) is guaranteed by membar_sync (rw/rw) - membar_release (rw/w) is guaranteed by membar_sync (rw/rw)
And, for the deprecated membars:
- membar_enter (whether r/rw, w/rw, or rw/rw) is guaranteed by membar_sync (rw/rw) - membar_exit (rw/w) is guaranteed by membar_release (rw/w)
(membar_exit is identical to membar_release, but the name is deprecated.)
Finally, while here, annotate some of the instructions with their semantics. For powerpc, leave an essay with citations on the unfortunate but -- as far as I can tell -- necessary decision to use lwsync, not isync, for membar_acquire and membar_consumer.
Also add membar(3) and atomic(3) man page links.
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1.7 |
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09-Apr-2022 |
riastradh |
sparc/membar_ops: Upgrade membar_enter from R/RW to RW/RW.
This will be deprecated soon but let's avoid leaving rakes to trip on with it arising from disagreement over the documentation (W/RW) and implementation and usage (R/RW).
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1.6 |
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09-Apr-2022 |
riastradh |
sparc: Fix membar_sync with LDSTUB.
membar_sync is required to be a full sequential consistency barrier, equivalent to MEMBAR #StoreStore|LoadStore|StoreLoad|LoadLoad on sparcv9. LDSTUB and SWAP are the only pre-v9 instructions that do this and SWAP doesn't exist on all v7 hardware, so use LDSTUB.
Note: I'm having a hard time nailing down a reference for the ordering implied by LDSTUB and SWAP. I'm _pretty sure_ SWAP has to imply store-load ordering since the SPARCv8 manual recommends it for Dekker's algorithm (which notoriously requires store-load ordering), and the formal memory model treats LDSTUB and SWAP the same for ordering. But the v8 and v9 manuals aren't clear.
GCC issues STBAR and LDSTUB, but (a) I don't see why STBAR is necessary here, (b) STBAR doesn't exist on v7 so it'd be a pain to use, and (c) from what I've heard (although again it's hard to nail down authoritative references here) all actual SPARC hardware is TSO or SC anyway so STBAR is a noop in all the silicon anyway.
Either way, certainly this is better than what we had before, which was nothing implying ordering at all, just a store!
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1.5 |
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06-Apr-2022 |
riastradh |
Nix trailing whitespace in files of membars, atomics, and lock stubs.
Will be touching many of these files soon for functional changes.
No functional change intended.
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Revision tags: cjep_sun2x-base1 cjep_sun2x-base cjep_staticlib_x-base1 netbsd-9-2-RELEASE cjep_staticlib_x-base netbsd-9-1-RELEASE bouyer-xenpvh-base2 phil-wifi-20200421 bouyer-xenpvh-base1 bouyer-xenpvh-base phil-wifi-20200411 is-mlppp-base phil-wifi-20200406 netbsd-8-2-RELEASE ad-namecache-base3 netbsd-9-0-RELEASE netbsd-9-0-RC2 ad-namecache-base netbsd-9-0-RC1 phil-wifi-20191119 netbsd-9-base phil-wifi-20190609 netbsd-8-1-RELEASE netbsd-8-1-RC1 pgoyette-compat-merge-20190127 pgoyette-compat-20190127 pgoyette-compat-20190118 pgoyette-compat-1226 pgoyette-compat-1126 pgoyette-compat-1020 pgoyette-compat-0930 pgoyette-compat-0906 netbsd-7-2-RELEASE pgoyette-compat-0728 netbsd-8-0-RELEASE phil-wifi-base pgoyette-compat-0625 netbsd-8-0-RC2 pgoyette-compat-0521 pgoyette-compat-0502 pgoyette-compat-0422 netbsd-8-0-RC1 pgoyette-compat-0415 pgoyette-compat-0407 pgoyette-compat-0330 pgoyette-compat-0322 pgoyette-compat-0315 netbsd-7-1-2-RELEASE pgoyette-compat-base netbsd-7-1-1-RELEASE tls-maxphys-20171202 matt-nb8-mediatek-base perseant-stdc-iso10646-base netbsd-8-base prg-localcount2-base3 prg-localcount2-base2 prg-localcount2-base1 prg-localcount2-base pgoyette-localcount-20170426 bouyer-socketcan-base1 pgoyette-localcount-20170320 netbsd-7-1-RELEASE netbsd-7-1-RC2 netbsd-7-nhusb-base-20170116 bouyer-socketcan-base pgoyette-localcount-20170107 netbsd-7-1-RC1 pgoyette-localcount-20161104 netbsd-7-0-2-RELEASE localcount-20160914 netbsd-7-nhusb-base pgoyette-localcount-20160806 pgoyette-localcount-20160726 pgoyette-localcount-base netbsd-7-0-1-RELEASE netbsd-7-0-RELEASE netbsd-7-0-RC3 netbsd-7-0-RC2 netbsd-7-0-RC1 netbsd-5-2-3-RELEASE netbsd-5-1-5-RELEASE netbsd-6-0-6-RELEASE netbsd-6-1-5-RELEASE netbsd-7-base yamt-pagecache-base9 yamt-pagecache-tag8 netbsd-6-1-4-RELEASE netbsd-6-0-5-RELEASE tls-earlyentropy-base riastradh-xf86-video-intel-2-7-1-pre-2-21-15 riastradh-drm2-base3 netbsd-6-1-3-RELEASE netbsd-6-0-4-RELEASE netbsd-5-2-2-RELEASE netbsd-5-1-4-RELEASE netbsd-6-1-2-RELEASE netbsd-6-0-3-RELEASE netbsd-5-2-1-RELEASE netbsd-5-1-3-RELEASE rmind-smpnet-nbase netbsd-6-1-1-RELEASE riastradh-drm2-base2 riastradh-drm2-base1 riastradh-drm2-base rmind-smpnet-base netbsd-6-0-2-RELEASE netbsd-6-1-RELEASE netbsd-6-1-RC4 netbsd-6-1-RC3 agc-symver-base netbsd-6-1-RC2 netbsd-6-1-RC1 yamt-pagecache-base8 netbsd-6-0-1-RELEASE yamt-pagecache-base7 netbsd-5-2-RELEASE netbsd-5-2-RC1 matt-nb6-plus-nbase yamt-pagecache-base6 netbsd-6-0-RELEASE netbsd-6-0-RC2 tls-maxphys-base matt-nb6-plus-base netbsd-6-0-RC1 yamt-pagecache-base5 yamt-pagecache-base4 netbsd-6-base netbsd-5-1-2-RELEASE netbsd-5-1-1-RELEASE yamt-pagecache-base3 yamt-pagecache-base2 yamt-pagecache-base cherry-xenmp-base bouyer-quota2-nbase bouyer-quota2-base matt-mips64-premerge-20101231 matt-nb5-mips64-premerge-20101231 matt-nb5-pq3-base netbsd-5-1-RELEASE yamt-nfs-mp-base11 netbsd-5-1-RC4 matt-nb5-mips64-k15 yamt-nfs-mp-base10 netbsd-5-1-RC3 netbsd-5-1-RC2 netbsd-5-1-RC1 rmind-uvmplock-base yamt-nfs-mp-base9 netbsd-5-0-2-RELEASE matt-nb5-mips64-premerge-20091211 matt-premerge-20091211 yamt-nfs-mp-base8 matt-nb5-mips64-u2-k2-k4-k7-k8-k9 matt-nb4-mips64-k7-u2a-k9b matt-nb5-mips64-u1-k1-k5 yamt-nfs-mp-base7 netbsd-5-0-1-RELEASE jymxensuspend-base yamt-nfs-mp-base6 yamt-nfs-mp-base5 yamt-nfs-mp-base4 jym-xensuspend-nbase yamt-nfs-mp-base3 netbsd-5-0-RELEASE netbsd-5-0-RC4 netbsd-5-0-RC3 netbsd-5-0-RC2 jym-xensuspend-base netbsd-5-0-RC1 netbsd-5-base matt-mips64-base2 wrstuden-revivesa-base-3 wrstuden-revivesa-base-2 wrstuden-revivesa-base-1 yamt-pf42-base4 yamt-pf42-base3 wrstuden-revivesa-base
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1.4 |
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25-May-2008 |
chs |
branches: 1.4.62; enable profiling of assembly functions.
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Revision tags: hpcarm-cleanup-nbase yamt-pf42-base2 yamt-nfs-mp-base2
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1.3 |
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28-Apr-2008 |
martin |
branches: 1.3.2; Remove clause 3 and 4 from TNF licenses
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Revision tags: yamt-pf42-baseX yamt-nfs-mp-base yamt-pf42-base yamt-lazymbuf-base15 yamt-lazymbuf-base14 hpcarm-cleanup-base keiichi-mipv6-base matt-armv6-base matt-armv6-nbase yamt-kmem-base3 cube-autoconf-base yamt-kmem-base2 yamt-kmem-base reinoud-bufcleanup-nbase reinoud-bufcleanup-base
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1.2 |
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29-Nov-2007 |
ad |
branches: 1.2.4; 1.2.8; Fix the aliases.
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1.1 |
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29-Nov-2007 |
ad |
sparc atomic ops
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1.5 |
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06-Apr-2022 |
riastradh |
Nix trailing whitespace in files of membars, atomics, and lock stubs.
Will be touching many of these files soon for functional changes.
No functional change intended.
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Revision tags: cjep_sun2x-base1 cjep_sun2x-base cjep_staticlib_x-base1 netbsd-9-2-RELEASE cjep_staticlib_x-base netbsd-9-1-RELEASE bouyer-xenpvh-base2 phil-wifi-20200421 bouyer-xenpvh-base1 bouyer-xenpvh-base phil-wifi-20200411 is-mlppp-base phil-wifi-20200406 netbsd-8-2-RELEASE ad-namecache-base3 netbsd-9-0-RELEASE netbsd-9-0-RC2 ad-namecache-base netbsd-9-0-RC1 phil-wifi-20191119 netbsd-9-base phil-wifi-20190609 netbsd-8-1-RELEASE netbsd-8-1-RC1 pgoyette-compat-merge-20190127 pgoyette-compat-20190127 pgoyette-compat-20190118 pgoyette-compat-1226 pgoyette-compat-1126 pgoyette-compat-1020 pgoyette-compat-0930 pgoyette-compat-0906 netbsd-7-2-RELEASE pgoyette-compat-0728 netbsd-8-0-RELEASE phil-wifi-base pgoyette-compat-0625 netbsd-8-0-RC2 pgoyette-compat-0521 pgoyette-compat-0502 pgoyette-compat-0422 netbsd-8-0-RC1 pgoyette-compat-0415 pgoyette-compat-0407 pgoyette-compat-0330 pgoyette-compat-0322 pgoyette-compat-0315 netbsd-7-1-2-RELEASE pgoyette-compat-base netbsd-7-1-1-RELEASE tls-maxphys-20171202 matt-nb8-mediatek-base perseant-stdc-iso10646-base netbsd-8-base prg-localcount2-base3 prg-localcount2-base2 prg-localcount2-base1 prg-localcount2-base pgoyette-localcount-20170426 bouyer-socketcan-base1 pgoyette-localcount-20170320 netbsd-7-1-RELEASE netbsd-7-1-RC2 netbsd-7-nhusb-base-20170116 bouyer-socketcan-base pgoyette-localcount-20170107 netbsd-7-1-RC1 pgoyette-localcount-20161104 netbsd-7-0-2-RELEASE localcount-20160914 netbsd-7-nhusb-base pgoyette-localcount-20160806 pgoyette-localcount-20160726 pgoyette-localcount-base netbsd-7-0-1-RELEASE netbsd-7-0-RELEASE netbsd-7-0-RC3 netbsd-7-0-RC2 netbsd-7-0-RC1 netbsd-5-2-3-RELEASE netbsd-5-1-5-RELEASE netbsd-6-0-6-RELEASE netbsd-6-1-5-RELEASE netbsd-7-base yamt-pagecache-base9 yamt-pagecache-tag8 netbsd-6-1-4-RELEASE netbsd-6-0-5-RELEASE tls-earlyentropy-base riastradh-xf86-video-intel-2-7-1-pre-2-21-15 riastradh-drm2-base3 netbsd-6-1-3-RELEASE netbsd-6-0-4-RELEASE netbsd-5-2-2-RELEASE netbsd-5-1-4-RELEASE netbsd-6-1-2-RELEASE netbsd-6-0-3-RELEASE netbsd-5-2-1-RELEASE netbsd-5-1-3-RELEASE rmind-smpnet-nbase netbsd-6-1-1-RELEASE riastradh-drm2-base2 riastradh-drm2-base1 riastradh-drm2-base rmind-smpnet-base netbsd-6-0-2-RELEASE netbsd-6-1-RELEASE netbsd-6-1-RC4 netbsd-6-1-RC3 agc-symver-base netbsd-6-1-RC2 netbsd-6-1-RC1 yamt-pagecache-base8 netbsd-6-0-1-RELEASE yamt-pagecache-base7 netbsd-5-2-RELEASE netbsd-5-2-RC1 matt-nb6-plus-nbase yamt-pagecache-base6 netbsd-6-0-RELEASE netbsd-6-0-RC2 tls-maxphys-base matt-nb6-plus-base netbsd-6-0-RC1 yamt-pagecache-base5 yamt-pagecache-base4 netbsd-6-base netbsd-5-1-2-RELEASE netbsd-5-1-1-RELEASE yamt-pagecache-base3 yamt-pagecache-base2 yamt-pagecache-base cherry-xenmp-base bouyer-quota2-nbase bouyer-quota2-base matt-mips64-premerge-20101231 matt-nb5-mips64-premerge-20101231 matt-nb5-pq3-base netbsd-5-1-RELEASE yamt-nfs-mp-base11 netbsd-5-1-RC4 matt-nb5-mips64-k15 yamt-nfs-mp-base10 netbsd-5-1-RC3 netbsd-5-1-RC2 netbsd-5-1-RC1 rmind-uvmplock-base yamt-nfs-mp-base9 netbsd-5-0-2-RELEASE matt-nb5-mips64-premerge-20091211 matt-premerge-20091211 yamt-nfs-mp-base8 matt-nb5-mips64-u2-k2-k4-k7-k8-k9 matt-nb4-mips64-k7-u2a-k9b matt-nb5-mips64-u1-k1-k5 yamt-nfs-mp-base7 netbsd-5-0-1-RELEASE jymxensuspend-base yamt-nfs-mp-base6 yamt-nfs-mp-base5 yamt-nfs-mp-base4 jym-xensuspend-nbase yamt-nfs-mp-base3 netbsd-5-0-RELEASE netbsd-5-0-RC4 netbsd-5-0-RC3 netbsd-5-0-RC2 jym-xensuspend-base netbsd-5-0-RC1 netbsd-5-base matt-mips64-base2 wrstuden-revivesa-base-3 wrstuden-revivesa-base-2 wrstuden-revivesa-base-1 yamt-pf42-base4 yamt-pf42-base3 wrstuden-revivesa-base
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1.4 |
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25-May-2008 |
chs |
branches: 1.4.62; enable profiling of assembly functions.
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Revision tags: hpcarm-cleanup-nbase yamt-pf42-base2 yamt-nfs-mp-base2
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1.3 |
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28-Apr-2008 |
martin |
branches: 1.3.2; Remove clause 3 and 4 from TNF licenses
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Revision tags: yamt-pf42-baseX yamt-nfs-mp-base yamt-pf42-base yamt-lazymbuf-base15 yamt-lazymbuf-base14 hpcarm-cleanup-base keiichi-mipv6-base matt-armv6-base matt-armv6-nbase yamt-kmem-base3 cube-autoconf-base yamt-kmem-base2 yamt-kmem-base reinoud-bufcleanup-nbase reinoud-bufcleanup-base
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1.2 |
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29-Nov-2007 |
ad |
branches: 1.2.4; 1.2.8; Fix the aliases.
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1.1 |
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29-Nov-2007 |
ad |
sparc atomic ops
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1.4 |
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25-May-2008 |
chs |
enable profiling of assembly functions.
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1.3 |
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28-Apr-2008 |
martin |
branches: 1.3.2; Remove clause 3 and 4 from TNF licenses
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1.2 |
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28-Nov-2007 |
ad |
branches: 1.2.4; 1.2.8; Fix the aliases.
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1.1 |
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28-Nov-2007 |
ad |
sparc atomic ops
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1.2.8.2 |
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03-Jun-2008 |
yamt |
sync with head
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1.2.8.1 |
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18-May-2008 |
yamt |
sync with head.
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1.2.4.2 |
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08-Jan-2008 |
matt |
sync with HEAD
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1.2.4.1 |
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28-Nov-2007 |
matt |
file membar_ops.S was added on branch matt-armv6 on 2008-01-09 01:21:08 +0000
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1.3.2.1 |
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22-Jun-2008 |
wrstuden |
Sync w/ -current. 34 merge conflicts to follow.
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